How to block an IP from accessing the admin folder?

My site had recently a huge and plolonged brute-force attack aimed on login.aspx page. Please could you advise on how to do these things:

= remove the login links from all the pages (I've tried this on the theme's site.master file but it caused an error due to the absence of aLogin element)
= rename the login directory (I've tried this but it caused an error. Will it be enough to define a new directory within the site.master.cs? But it has to be done together with the above.)
= restrict the access to the login directory for all IPs except mine ones. (I've tried this solution:http://www.stokia.com/support/misc/web-config-ip-address-restriction.aspx
but it caused the 500 error.

Or to make this folder passwod protected (I can do it via control panel on the hosting)?
And which one of these loads the sever less (I'm on a shared hosting and BE 2.0)?